Question Old computer suddenly won't output a signal to the monitor ?

[Easterlily]

So... I bet there are a ton of threads that are similar to my case, but I've spent the whole day reading around and trying different solutions and still am only left with a headache.

So we have this computer at work thats around 10 years old and runs on Windows 7. We use software that is not compatible with newer operating systems and therefore haven't upgraded it or replaced it.

The computer has worked fine until this morning when one of the softwares locked up and froze. My colleagues solution was to pull the power cord and restart the computer. When trying to start the computer again, the fans start and the power indicator lights up but the computer won't give any video signal. The keyboard buttons won't light up (caps lock for instance). No bios or logos, nothing.

So these are the things I've tried:
- changing RAM spot
- replacing the RAM with a similar one
- trying the RAM from the faulty computer in a working one (the ram works fine)
- pull out and push in all the power cords to the motherboard.
- replacing VGA cord and also trying with a dvi to HDMI adapter. (Also tested both cables on a working computer).
- trying a different monitor
- remove the cr2032 battery, pull out the power cord and hold the start button. Leaving the computer unplugged for a few minutes.
- installing a fresh 2032 battery
- tried connecting the faulty computers power supply to a working computer (works fine)
- tried connecting a working computers power supply to the faulty computer (same problem).
- remove the cooler and the processor, checking for any damage (processorn looks fine and gets hot when in use (tried touching it without the cooler installed)).
- tried connecting the faulty computers hard drive to another computer. It's not possible to boot from the hard drive (I guess because of locked windows license?), the boot option won't show up anyway. However if I plug it in on a working Windows computer, I am able to browse the files.

So basically I was ready to give up. But then suddenly I get a signal to the monitor showing the specifications of the system, telling me the CPU fan was not working and asking me to press F1 for setup. I quickly plug in my usb keyboard and press F1, but the computer soon shuts itself off. Most likely since I did not have the CPU cooler installed at the time and the processor got overheated.

So somehow the computer suddenly started to kind of work. And now I can't drop this.

What do you guys think?

 

[Easterlily]

I should add. At the time I got the video signal I had just removed the CPU cooler and also removed the CMOS battery. So the battery was out when I got the signal. But I have tried to mirror this scenario without any luck.

 

[SkyNetRising]

then suddenly I get a signal to the monitor showing the specifications of the system, telling me the CPU fan was not working and asking me to press F1 for setup. I quickly plug in my usb keyboard and press F1, but the computer soon shuts itself off. Most likely since I did not have the CPU cooler installed at the time and the processor got overheated.
So somehow the computer suddenly started to kind of work. And now I can't drop this.

What do you guys think?

1st - list full specs of your system.

2nd running a pc without cpu cooler is a big no-no.
On older systems cpu would literally start smoking and in some situations even explode, if you did that.

View: https://youtu.be/Xf0VuRG7MN4?t=54

 

[Easterlily]

1st - list full specs of your system.

2nd running a pc without cpu cooler is a big no-no.
On older systems cpu would literally start smoking and in some situations even explode, if you did that.

View: https://youtu.be/Xf0VuRG7MN4?t=54

Yeap you're absolutely right. It was only for a short while though. Not longer than a minute tops. Hopefully the CPU wasn't damaged, but to be honest I was positive the computer was beyond repair and that's why I tried feeling if the CPU heated up. (In my head, a dead CPU would be cold).

I don't know the specs on the computer at this moment but will try to see if I can see any labels tomorrow.
For now the best I can give you:
It's a basic pre built office computer.
One ddr3 memory at 4gb, 12800.
500gb Seagate harddrive.
Motherboard with only VGA and dvi built in graphics.
No idea what CPU it is at this time.
Cooler master basic CPU cooler.

This info probably doesn't help much.

 

[Easterlily]

Update:
The computer is an HP Pro 3515
See: https://support.hp.com/rs-en/document/c03544621
Motherboard: MS-7778

Today I tried even another PSU (i noticed that the one i tried yesterday from a known working computer had lower wattage, so i figured maybe its not sufficient) but no difference.
I also tried removing the whole motherboard from the case and put it on a wooden table together with the original PSU. No difference.

I examined the motherboard but I cannot see any obvious wear (iex burn marks).

Any ideas, or is it straight to the trashbin?